Method for determining position with improved calibration with opposing sensors

ABSTRACT

The method and system for determining position with improved calibration allows a device to initiate activity at the proper location, such as navigating a drill bit through a rock formation. A pair of position sensors in opposite orientations generates position data signals. A temperature sensor detects temperature and duration of the temperature. An adjusted plastic bias value is determined by a processor module based on the temperature data signal, the duration of the temperature, and the position data signals so as to account for bias and hysteresis errors and error correction based on the opposing orientations of the pair of position sensors. A position value is set according to the adjusted plastic bias value so that the position value is more accurate. The activity of the terminal device is initiated or maintained according to the position value calibrated by the adjusted plastic bias value.

CROSS-REFERENCE TO RELATED APPLICATIONS

See also Application Data Sheet.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

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INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC OR ASA TEXT FILE VIA THE OFFICE ELECTRONIC FILING SYSTEM (EFS-WEB)

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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINTINVENTOR

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BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to determining position of a tool foroperations at a location of the tool. In particular, the presentinvention relates to calibrating sensors for determining position of thesensors. Even more particularly, the present invention relates tocalibrating sensors on a downhole tool to more accurately determineposition of the downhole tool in an underground formation, such thatsetting location of activity or operations, such as drilling by thedownhole tool, is more accurate.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 37 CFR 1.98

Sensors to determine position are used in a tremendous number ofimportant processes, such as deployment of vessels in space, movement ofa video game controller, and injection of cells in a tumor. On largescales and small scales, determining position for operations at thedetermined position can be very important. Accurate sensors are crucialfor the performance of those activities. Sensors are also known todirect oil and gas operations in a rock formation. The direction of thetool and the location of the wellbore are detected, so that the variousdownhole activities can be accurately placed in the formation. Thesedownhole activities include drilling, injecting, and isolating zones inthe formation. The accuracy of the sensor and placement of a wellborecan seriously affect the outcome of a drilling operation.

Sensors are calibrated to increase the amount of accuracy and precisionso that the determination of position is also as accurate and precise aspossible. Sensors in extreme environmental conditions are subject toerror, due to those conditions, such as high temperatures. Theenvironment of a sensor can include the depth, pressure and heat in awellbore. Alternative environments for accelerometers also include hightemperatures from electronic components in a circuit board of a videogame controller, re-entry heat in orbit, and elevated temperatures fromradiation treatment in cellular tissue

In the prior art, redundancy is used for increasing accuracy. U.S. Pat.No. 6,206,108, issued to MacDonald, et al. on Mar. 27, 2001, teaches amethod for adjusting a drilling operation based on a system withmultiple sensors to measure multiple parameters. The sensors correcteach other, and each sensor measurement further refines an instrumentreading downhole. In U.S. Patent Application No. 2010/0078216, publishedfor Radford, et al. on Apr. 1, 2010, a system and method for downholevibration monitoring for reaming tools includes a plurality ofaccelerometers, a plurality of magnetometers, and at least onetemperature sensor. The plurality of accelerometers corrects or verifiesother sensors to guide drilling. U.S. Pat. No. 6,648,082, issued toSchultz, et al. on Nov. 18, 2003, teaches a method for differentialsensor measurement and a system to detect drill bit failure. The systemincorporates a main sensor and individual sensors for other sensorvalues, which are compared to each other to create a self-correctingsystem.

The prior art further establishes mathematical models to increaseaccuracy. U.S. Pat. No. 8,818,779, issued to Sadlier, et al. on Aug. 26,2014, teaches a system and method for real-time wellbore stability whiledrilling a borehole. The drilling operation is adjusted in real timeaccording to sensor readings compared against a geomechanical model.U.S. Patent Application No. 2014/0231141, published for Hay, et al. onAug. 21, 2014, discloses a system and method for automatic weight on bitsensor correction with a sensor arranged in a bottomhole assembly. Themethod comprises first taking a survey recording an initial depth withina borehole, calculating a prediction borehole curvature at a seconddepth, calculating a weight correction value based on the predicted holecurvature, and finally adjusting the borehole position with the weightcorrection value.

Adjusting for accuracy in the prior art focuses on external factors andconditions affecting readings, not the sensor itself. The mathematicmodels apply to a specific context for drilling operations, not thegeneral accuracy and precision of the sensor. In a different context fora different activity (deep space, microsurgery), there is still a needto calibrate according to the components of the sensor itself.

The factory calibration of a sensor is addressed in the prior art. Uponassembly, the components of the sensor are calibrated before applied ina specific context with other distorting external conditions. U.S. Pat.No. 5,880,680, issued to Wisehart, et al. on Mar. 9, 1999, teachescalibration of a sensor according to a temperature model. Oneaccelerometer is tested at the time of manufacture to determine atemperature model of how accuracy of the accelerometer is affected atdifferent temperatures. In the drilling operation, a temperature sensorand the accelerometer are run in the wellbore, and the readings of theaccelerometer and the readings from the temperature sensor are processedaccording to the temperature model. U.S. Pat. No. 7,234,540, issued toEstes, et al. on Jun. 26, 2007, teaches a system and method of atwo-axis gyroscope and other sensors which, when incorporated into abottomhole assembly, determines the direction of the wellbore anddrilling tool in real-time. A number of corrective operations areapplied to the sensors while downhole, including a scale factorcorrection for the temperature at the final position.

The prior art general calibration requires numerous measurements takenover many sensor orientations and temperatures, and the prior artmethods only account for temperature affecting components of thesensors. However, temperature is not the only factor, especially forcertain types of sensors.

The relative position of sensors has also been used to account forerror. It is known to align solid state sensors in pairs and ondifferent axes together. U.S. Pat. No. 6,767,758, issued to Geen on Jul.27, 2014, teaches micro-machined multi-sensor system which provides oneaxis of acceleration sensing and two axes of angular rate sensing. Thesensor includes a pair of accelerometers. Each accelerometer includes apair of sense electrodes on the lateral axis and the longitudinal axis.U.S. Pat. No. 7,571,643, issued to Suguira on Aug. 11, 2009, teaches asystem and method for downhole dynamics measurements which incorporatesa sensor arrangement for measuring downhole dynamic conditions and mayinclude a tri-axial arrangement of accelerometers within the housing.The MEMS solid state sensors are set in pairs on the x, y and z axes.The term “diametrically opposed” is used to describe a cancelling outeffect of the arrangement.

Sensor positions are used for multiple reasons, including increasingdata collection and triangulation from signals. Seismic signals andacoustic sensors can triangulate the readings. The data collection froman array uses the different relative locations of the sensors incalculations. U.S. Pat. No. 7,424,928, issued to Cox, et al. on Sep. 16,2008, teaches a system and method for flexibly coupling sensors to adownhole tool for measuring seismic data, by isolating seismic receiversfrom vibrations in the drill string and enabling the differentiation ofcompression waves from shear waves. U.S. Patent Publication No.2013/0070560, published for Zheng, et al. on Mar. 21, 2013, discloses asystem and method for an acoustic tool with a sensor array. The sensorsin the array are arranged back to back. The sensors are placed totriangulate the received signal. U.S. Patent Publication No.2005/0150689, published for Jogi, et al. on Jul. 14, 2005, discloses asystem and method for enhancing directional accuracy and control usingbottomhole assembly measurements. There are two sensors taking differentmeasurements of a bending signal on different axes. An estimate iscalculated in order to predict borehole curvature. The sensors areplaced in different orientations for more relevant data collection.

Collecting additional confirmation data for increased precision is priorart. U.S. Pat. No. 5,058,077, issued to Twist on Oct. 15, 1991, teachesa compression technique for generating a corrected well log which couldinclude erroneous signals from a downhole sensor. The sensors are placedlongitudinally and radially about the drill collar in order to obtainthe advantage of the phase angle difference between pairs of sensors andthe relative orientation and position of the tool within the borehole.U.S. Pat. No. 5,842,149, issued to Harrell, et al. on Nov. 24, 1998,teaches a system and method for a closed loop drilling system includingmultiple sensors which are used within the system to retrieve signalswhich are then compared to programmed instructions and models, andfinally used to allow the system to automatically adjust to the newdrilling parameters. Sensors are positioned for data collection, notcalibration or error correction.

More modern accelerometers are small micro electro-mechanical systems(MEMS or micro-mechanical systems, MMS). One of the most simple and lessexpensive MEMS devices is an open loop MEMS device, which basicallyconsists of a hinged micro machined silicon wafer. The silicon wafer isthe sensing element that moves in the presence of a gravitational fieldor acceleration force. The open loop MMS sensor measures the departurefrom a neutral starting position of the wafer. Another MEMS device is aclosed loop MEMS device basically consisting of a cantilever beam, suchas a cantilever beam, and a proof mass on the beam. The cantilever beamcan be maintained in a neutral zero force position by applying a currentflow through a small magnetic element, which creates the exact force toneutralize the gravitational force acting on the cantilever beam. Anadditional amount of current is applied proportionally to thegravitational field vector being measured in a particular orientation asrequired to keep the cantilever beam in the neutral position. A magneticforce induced by the electric current returns the cantilever beam to thestart or neutral position. Thus, by measuring the amount of current toreturn the cantilever beam to the neutral force position, the amount ofacceleration force or gravitational force can be measured. The presentinvention is applicable to both open loop and closed loop sensors. Thereis particular utility for open loop sensors with the present invention.

The errors from MMS sensors can originate from bias and hysteresis typedistortion. Bias error happens because the cantilever beam is deformedby high temperatures and cannot return to the same neutral/null positionwith the same voltage. Hysteresis type distortion happens because theamount of deformation of the cantilever beam by high temperaturesrelates to the time spent at the high temperatures. The physicalcomponent, such as the silicon wafer and cantilever beam, furtherdeforms from being exposed to the repeated higher and lower temperaturesfor different amounts of time. These components of the MEMSaccelerometer are affected by additional errors, besides the temperatureitself. The past effects of high temperature are not addressed in thecurrent calibration methods, which have particularly high impact on MEMSaccelerometers.

Bias errors and hysteresis errors are known for prior artaccelerometers. The '540 patent also includes a bias correction, whichis obtained from a prior survey; and misalignment and gravity dependentcorrections to the gyroscope axes. Use of a sensor will have biaserrors, as the components drift when the sensor is in use. However, theMMS sensors, in particular open loop MMS sensors, are more susceptibleto bias errors and hysteresis errors, especially with exposure to hightemperatures over extended periods of time. MMS sensors can becalibrated according to the prior art, including attempts at biascorrection; however, the prior art for regular accelerometers does notaddress MMS sensors, which are more prone to these errors than regularaccelerometers. The sensitivity and durability for the components of MMSsensors are not the same as traditional accelerometers. The oldsolutions for error of the prior art can apply to MMS sensors, but thoseold solutions are not sufficient for reliability. Additional solutionsare required for the MMS sensors to be used repeatedly in hightemperature conditions.

The accuracy problem of MMS sensors is known, and the shortcomings of afactory temperature model calibration is also known. U.S. Pat. No.7,168,507, issued to Downton on Jan. 30, 2007, teaches a system andmethod for recalibrating downhole sensors by comparing output values oftwo sets of sensors. The first set of sensors is inexpensive andcomprised of less accurate MMS sensors, so they are placed close to thedrill bit with a high risk of damage. The second set of sensors isexpensive and placed in a more stable remote location. The second set ofsensors are accelerometers measuring the same parameters, when thesecond set arrives at the same location where the first set tookmeasurements. The first set of MMS sensors are calibrated by thereadings from the second set. Instead of solving the reliability problemof the MMS sensors, the prior art solution is to retain a second set ofthe more expensive accelerometers to double check the MMS sensors. The'507 patent acknowledges the known error rate of inexpensive MMSsensors, but the solution of adding a second expensive set of moreaccurate sensors remains expensive and redundant.

It is an object of the present invention to provide a method fordetermining position with improved calibration.

It is another object of the present invention to provide a method fordetermining position of a tool or a terminal device at a location forinitiating activity.

It is still another object of the present invention to provide a methodfor initiating activity at a particular location determined by acalibrated sensor.

It is an object of the present invention to calibrate a sensor.

It is another object of the present invention to calibrate an MMSsensor.

It is still another object of the present invention to calibrate an MMSsensor for a bias correction.

It is yet another object of the present invention to calibrate an MMSsensor for a hysteresis correction.

It is another object of the present invention to provide a method fordetermining position with improved calibration of an MMS sensor.

It is still another object of the present invention to provide a methodfor initiating activity at a particular location determined by acalibrated MMS sensor.

It is an object of the present invention to provide a method forgenerating a plastic bias value for calibrating an MMS sensor.

It is another object of the present invention to provide a method fordetermining a plastic bias value based on temperature, time duration ata temperature, and gravity.

It is an object of the present invention to provide a method forgenerating an orientation bias value for correcting sensor readings oftwo MMS sensors in opposite orientations.

It is another object of the present invention to provide a method fordetermining an orientation bias value based on temperature, timeduration at a temperature, and position of each MMS sensor.

It is an object of the present invention to calibrate a sensor after afactory calibration of the sensor.

It is an object of the present invention to calibrate a sensor with aplastic bias value concurrently with a factory calibration of thesensor.

It is an object of the present invention to continuously calibrate asensor according to an adjusted plastic bias value continuouslygenerated by each position data signal.

It is another object of the present invention to provide a method fordetermining position with a continuous calibration of an MMS sensor.

It is still another object of the present invention to provide a methodfor initiating and maintaining activity at particular locationsdetermined by a continuously calibrated MMS sensor.

These and other objectives and advantages of the present invention willbecome apparent from a reading of the attached specification.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include the method and system fordetermining position with improved calibration. Any device requiringaccurate position data can determine location of the device with asensor calibrated according to the present invention. The location andorientation of the device can be more accurately detected, so that thedevice can initiate or maintain activity in the desired location andorientation. Furthermore, the position data can be calibrated in realtime so that a device can be actively guided, such as navigating a drillbit, while drilling through a rock formation.

The method of the present invention includes assembling a first positionsensor comprised of a first oscillation element having a first range ofdisplacement in a first set direction according to gravity in a firstorientation and a second position sensor comprised of a secondoscillation element having a second range of displacement in a secondset direction according to gravity in a second orientation. The firstand second orientations are opposite each other. Each position sensorcan be an accelerometer of MMS sensor. One embodiment includes eachposition sensor being an MMS sensor exposed to high temperatureconditions. A corresponding position data signal is generated based onan amount of displacement in the set direction, and a temperature datasignal is detected by a temperature sensor in proximity, in some casesclose proximity, to the position sensors. The position data signals andtemperature data signal are communicated to a processor module incommunication with the position sensors and the temperature sensor. Aposition value is generated by the processor module based on theposition data signals, the temperature data signal, and duration of atemperature of the temperature data signal. The position value is basedon temperature and gravitational force, including how many times and howlong the position sensors are exposed to the temperature conditions. Thedata signals and values are stored in the memory module. The positionvalue is communicated to the terminal device so that activity of theterminal device corresponds to the position value.

The step of generating the position value further comprises generatingan adjusted plastic bias value to set the position value, so that theposition value accounts for bias and hysteresis errors and improvesaccuracy of the position value. The plastic bias value relates thetemperature data signal, the duration of the temperature, and theposition data signals, according to bias and hysteresis of theoscillation element of the position sensor. There is additional errorcorrection based on the differences between the first position datasignal and the second position data signal due to gravity. The methodaccounts for the bias error of the component of each position sensor,relative to temperature, the hysteresis error of the component of eachposition sensor, relative to duration of temperature, and theorientation of the gravitation field. The adjusted plastic bias valuecan at least partially cancel out hysteresis errors and other errors dueto the electronics, physics and chemistry of the sensing element.Additionally, the adjusted plastic bias value correction to the positionvalue is a continual temporal additional correction to the originalsensor bias calibration factor. Note the plastic bias correction isapplied to each one of the opposing sensors. In the present invention,the position data signals can be corrected so that measurements ofgravity on the oscillation element and capacitance (open loop) orcurrents (closed loop) of the position sensors are corrected to the setposition value.

The present invention can be continuous, unlike prior art sensors withonly an initial or factory calibration. The step of generating theposition data signals and generating the position value according to anadjusted plastic bias value can be repeated over and over.Alternatively, the step of generating the position data signals andsetting the position value can comprise generating a plurality of thedata signals and setting the corresponding plurality of position datasignals according to the respective plurality of adjusted plastic biasvalues.

Embodiments of the system of the present invention include the firstposition sensor, the second position sensor, the temperature sensor,processor module, memory module and terminal device. The terminal devicecan be any device requiring position data for operation, such as adownhole tool in the oil and gas industry, a survey tool for mappinglocations, or a mobile probe for tracking location of the sensor or avideo game controller for translating movements into game action. Thepresent invention can include any terminal device that uses location andorientation data. In some embodiments, the position sensors can be MMSsensors exposed to high temperatures. The system can also includeanother pair of position sensors generating another pair of positiondata signals and another position value adjusted according to anotheradjusted plastic bias value. The multiple sensor pair embodiment canfurther reduce errors and confirm accuracy of location and orientation.The system can also include at least one magnetometer in proximity tothe temperature sensor. The field data signals from the magnetometer canbe used to determine calculated parameters, such as compass azimuth andthe earth's magnetic dip. These parameters use both the field datasignals as magnetometer magnetic signals and position data signals asaccelerometer gravitational signals, such that these parameters can alsobe improved with the plastic bias value of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view of the system of the present invention,showing the terminal device as a drilling and activity as drilling in afirst orientation.

FIG. 2 is another schematic view of the system of the present invention,showing the terminal device as a drilling and activity as drilling in asecond orientation.

FIG. 3 is a flow diagram of an embodiment of the method of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1-3, the present invention includes the method andsystem 10 for determining position of a device 20 with improvedcalibration of a first position sensor 30 and a second position sensor30′ of the device. The location and orientation of the device 20 aremore accurate with the present invention. The position sensors 30, 30′calibrated according to the present invention allow the device 20 toproperly initiate or maintain activity in the intended location andorientation. When calibrated in real time, the device 20 can be activelyguided, such as navigating a drill bit 22, while drilling through a rockformation. Errors due to bias and hysteresis can be reduced by themethod and system of the present invention. Previous sensors with largebias and hysteresis errors, such as MMS sensors exposed to hightemperatures, in particular open loop devices, can now be incorporatedinto devices for reliable determination of position data. Errors due togravity and a gravitational field can also be reduced by the method andsystem of the present invention. The error correction for bias andhysteresis are further modified by the adjustment according toconsideration of gravity in opposing orientations.

FIGS. 1-2 show the system 10 including a first position sensor 30, asecond position sensor 30′, a temperature sensor 40, a processor module50, a memory module 60 and a terminal device 20. The terminal device 20can be any device requiring position data for operation, such as adownhole tool with drill bit 22 in the oil and gas industry, as in FIGS.1 and 2, a survey tool for mapping locations, or a mobile probe fortracking location of the sensor or a video game controller fortranslating movements into game action. In FIGS. 1-2, the device 20 is adownhole tool with a drill bit 22. In this embodiment, the activity isdrilling with the drill bit 22. The present invention can include anyterminal device that uses location and orientation data.

The first position sensor 30 is comprised of a first oscillation elementhaving a first range of displacement in a first set direction accordingto gravity in a first orientation. The second position sensor 30′ iscomprised of a second oscillation element having a second range ofdisplacement in a second set direction according to gravity in a secondorientation. FIGS. 1-2 show the first oscillation element relative togravity (G) and horizontal (H) and the second oscillation elementrelative to gravity (G′) and horizontal (H′). In FIG. 1, the first setdirection (X) is shown horizontal and matching horizontal (H) in thefirst orientation of the first position sensor 30. The second setdirection (X′) is also shown horizontal and matching horizontal (X′) inthe second orientation, opposite the first orientation. Gravity affectsboth sensors the same, but in opposite directions.

In FIG. 2, the first set direction (X) is shown at a pitched angle tohorizontal (H) and the second set direction (X′) is also shown at apitched angle to horizontal (H′). Gravity on the second oscillationelement of the second position sensor 30′ is no longer the same as thefirst oscillation element of the first position sensor 30. The force ofgravity is no longer equal nor directly opposite the first positionsensor 30.

The accurate determinations of X and X′ determine the orientation of thedevice 20 or downhole tool, so that the drilling of the drill bit 22 ison the correct path. The first position sensor 30 and second positionsensor 30′ generate respective first and second position data signalsfor what the respective oscillation elements detect as X and X′. Themechanical limitations of each oscillation element affect accuracy ofthe detected X and X′ data signal as the actual X of the device 20.FIGS. 1 and 2 also show the temperature sensor 40 for detecting atemperature data signal and being in proximity to the first positionsensor 30 and second position sensor 30′. The environmental conditionsexperienced by the first position sensor 30 and second position sensor30′ match the temperature sensor 40. The effect of temperature on thefirst position sensor 30 and the second position sensor 30′ is detectedby the temperature sensor 40.

In some embodiments, the position sensors 30 and 30′ can be MMS sensorsexposed to high temperatures. FIGS. 1-2 show the device 20 as a downholetool. The environmental conditions of using the downhole tool includeextreme temperatures and pressures. The mechanical components must bedurable and resilient because retrieval for repair is not a simple taskat great depths in the rock formation. Prior art quartz accelerometershave been used for downhole tool. However, the costs and spacerequirements for these accelerometers as position sensors are demanding.The present invention allows the MMS sensor to replace a quartzaccelerometer without losing accuracy and durability.

FIGS. 1-2 show the schematic illustrations of the processor module 50being in communication with the position sensor 30 and the temperaturesensor 40. The processor module 50 receives the position data signalsfrom both the first position sensor 30 and the second position sensor30′ and the temperature data signal by transmission or by hard wiring.The processor module 50 generates a position value based on the positiondata signals for what the first position sensor 30 detected as X, whatthe second position sensor 30′ detected as X′, and the temperature datasignal. The memory module 60 is also a schematic illustration incommunication with the processor module for storing the position datasignals, the temperature data signal, and the position value.

The terminal device 20 is shown in communication with the processormodule to receive the position value. There can be a control means 24for activity corresponding to the position value. FIGS. 1-2 show aschematic control means 24 for the drilling action of the drill bit 22.In the present invention, there can be other devices, control means andactivities. For example, the terminal device can be survey tool with theactivity being mapping or a mobile probe with the activity beingtracking or a video game controller with the activity being gamemovement in a virtual reality.

FIGS. 1-2 also show various alternate embodiments. There can be anotherpair of position sensors 32, 32′, each being comprised of anotheroscillation element having another range of displacement in another setdirection according to gravity in another opposite orientationarrangement. FIG. 1 shows the pair 32, 32′ in the same opposingorientation at position sensors 30, 30′ for comparison data to positionsensors 30, 30′. FIG. 2 shows the pair 32″, 32′″ in a different opposingorientation relative to position sensors 30, 30′. The data from thispair 32″, 32′″ can contrast and confirm some of the gravity inducederror of the position sensors 30, 30′.

The other position sensors 32, 32′, 32″, 32′″ are also in proximity tothe position sensors 30, 30′ and the temperature sensor 40, so that theother position data signals generated remain comparable to the positiondata signals of the position sensors 30, 30′. The other pair of positionsensors 32, 32′ is in communication with the processor module 50, sothat the position value is determined by the position data signal fromthe position sensors 30, 30′, the pair of other position data signalsfrom the other pair of position sensors 32, 32′, and the temperaturedata signal for further error reduction and confirmation of the detectedposition data of location and orientation.

A magnetometer 80 in proximity to the temperature sensor 40 and incommunication with the processor module 50 is also shown in FIGS. 1-2.The magnetometer 80 generates a field data signal, which can also beused by the processor module 50 to determine an additional positionvalue, such as compass azimuth or earth's magnetic dip. The plastic biasvalue for correcting the position data signal, the position datasignals, and the field data signal, corresponding to magnetic fieldstrength, determine the additional position value. Thus, the additionalposition value, such as azimuth, is now more accurate because of theplastic bias value. In some embodiments, there can be more than onemagnetometer, such as magnetometer 82, to further compare and confirmthe additional position values from other field data signals.

Referring to FIG. 1-3, the present invention includes the method andsystem 10 for determining position of a device 20 with improvedcalibration of a first position sensor 30 and a second position sensor30′ of the device. The location and orientation of the device 20 aremore accurate with the present invention. The first position sensor 30and the second position sensor 30′ calibrated according to the presentinvention allows the device 20 to properly initiate or maintain activityin the intended location and orientation. When calibrated in real time,the device 20 can be actively guided, such as navigating a drill bit 22,while drilling through a rock formation. Errors due to bias andhysteresis can be reduced by the method and system of the presentinvention. Errors due to gravity measurement can be reduced whenaccounting for the bias and hysteresis errors of the present invention.Previous sensors with large bias and hysteresis errors, such as MMSsensors exposed to high temperatures, can now be incorporated intodevices for reliable determination of position data.

The method of the present invention includes assembling position sensors110 in opposing orientations. Each position sensor is comprised of anoscillation element having a range of displacement in a set directionaccording to gravity. The position sensors can be quartz accelerometersor MMS sensors. One embodiment includes each position sensor being anMMS sensor exposed to high temperature conditions with an oscillationelement, such as the silicon micro machined wafer of an open loop sensorsystem or a cantilever beam of a closed loop sensor system. The wafer orcantilever beam is affected by gravity or acceleration forces, so thereis an amount of displacement of the wafer or an amount of current in aparticular orientation required to keep the cantilever beam in place.Thus, the amount of displacement or the amount of current and directionof current reveals the amount and direction of acceleration. The errorsfrom this type of MMS sensor can originate from bias and hysteresis typedistortion. Bias error happens because the oscillation element (wafer orcantilever beam) is deformed by high temperatures and cannot return tothe same neutral/null position with the same current induced magneticforce. Hysteresis type distortion happens because of a latency andphysical/chemical sticking in the oscillation element's ability to fullyrecover from temperature fluctuations and reversals. The oscillationelement further deforms from being exposed to the repeated higher andlower temperatures for different amounts of time. The force of gravityalso affects the distortion of the oscillation element (wafer orcantilever beam). In opposite orientations, the effect of gravity can besubtracted out or at least partially subtracted out, so that thedistortion of position data signals does not remain in the positionvalue generated by the processor module.

Position data signals are generated 120 based on each amount ofdisplacement of the respective oscillation element in the respective setdirection. In the embodiments with the wafer and cantilever beam, eachposition data signal corresponds to the measurement of gravity on thewafer or the cantilever beam, respectively. The capacitance measurementof the displacement of the silicon wafer can determine the position datasignal for location and orientation for an open loop system. The currentrequired to maintain the cantilever beam can determine the position datasignal for location and orientation for a closed loop system. Thisposition data signal is not a true position value, so the position datasignal requires correction to a more accurate position value because thebias and hysteresis errors affect the accuracy of these sensor readingsand because gravity distorts the respective oscillation elements in thefirst orientation and in the second orientation.

The prior art calibrations correct for temperature distortions, but notdistortions due to changes in the components of the sensor themselves.When delicate components, such as oscillation elements in MMS sensors,are assembled for compact size, lower costs, and lighter weights of theposition sensor, the prior art calibrations fail to adequately correctthe position data signals. The smaller, lighter, and cheaper positionssensors cannot be used in devices that require high levels of accuracy.

In the method of the present invention, a temperature data signal isdetected 130 by a temperature sensor in proximity to the positionsensors. The device will have both the position sensors and temperaturesensor exposed to the same conditions, such as the same temperatures,but the orientations relative to gravity will be opposed. The positiondata signals and temperature data signal are communicated to a processormodule 140 in communication with the position sensors and thetemperature sensor. The sensors and processor module can be connected sothat data can be exchanged between these components. There is also amemory module in communication with the processor module.

The processor module generates a position value 150 based on theposition data signals, the temperature data signal, and duration of atemperature of the temperature data signal. The position value canaccount for temperature distortions, gravity distortions, biasdistortions and hysteresis distortions. The amount of time the positionsensor is exposed to the temperature of the temperature data signal isused to determine the position value. The present invention includesmore than the temperature alone to set the position value of the device.

Next, the position data signals, the temperature data signal, durationof the temperature and the position value are stored in the memorymodule 160, and the position value is communicated to the device 170 sothat activity of the device can correspond to the position value. Whenthe position of the device is accurately determined, the activity can beinitiated 180 in the correct place. In the example of the drill bit asthe device or terminal device, drilling with the drill bit at theaccurate location in the rock formation is very important for placingthe wellbore in the right location for access to production zones in therock formation. Missing the location has serious consequences for thesuccess of the hydrocarbon production. In the example of the video gamecontroller, the motion of the controller must correspond accurately tomovement on the video display. In the example of a mobile probe, thelocation of the mobile device must be accurate for tracking movement ofthe mobile device.

Embodiments of the step of generating the position value of the presentinvention further comprise generating a plastic bias value 152 tocorrect the position data signals for the actual X of the device. Theplastic bias value relates the temperature data signal, the duration ofthe temperature, and the position data signals, according to bias andhysteresis of the oscillation element of the position sensor. The methodaccounts for the bias error of these mechanical components of eachposition sensor 154, affected by exposure to temperature, and for thehysteresis error of these mechanical components of each position sensor156, affected by duration and fluctuation of exposures to thetemperature conditions. The position value is set by the plastic biasvalue 158 for a more accurate position value corresponding to the actualX of the device.

For each linear sensor, a prior art sensor calibration might bedescribed by equation:CAL=[RAW*SCALE(t)]−BIAS(t)  (Equation 1)

-   -   wherein CAL is the prior art calibrated sensor reading or prior        art position value,    -   wherein RAW is the original sensor reading or position data        signal, SCALE(t) is a scale factor that is a function of        temperature, and BIAS(t) is a bias factor that is a function of        temperature. In the case of this prior art calibration, SCALE(t)        and BIAS(t) can be determined by experimentation before the        sensor is put into use. The prior art calibration is the factory        calibration after the sensors are assembled.

For the present invention, the step of generating the position value isdescribed by:CAL=[RAW*SCALE(t)]−BIAS(t)  (Equation 1)andCAL′=CAL−PLASTIC_BIAS(temperature,CAL,time)  (Equation 2)

-   -   wherein CAL′ is the improved, calibrated sensor reading for the        position value of the present invention, and wherein        PLASTIC_BIAS(temperature, field, time) is the Plastic Bias term        or plastic bias value, which is a function of temperature, field        and time. Field can refer to the position data signal or other        measurement dependent on gravity. In Equation 2, CAL refers back        to the calculation of the prior art position value determined by        the position data signal (RAW). This new PLASTIC_BIAS term        cannot be determined before the sensor is put to use. The        plastic bias value can be active and continuous during use based        on the actual sensor environment.

In the present invention, the position value requires furthermodification. As a function of temperature, gravitational field andtime, wherein “field” can refer to the position data signal or othermeasurement dependent on gravity, the orientation in gravity matters.Bending, with the help of gravity, especially with high sensitivity athigh temperatures, can affect the accuracy of the position data signal.To remove “the help of gravity”, the method further set the positionvalue by adjustment according to opposing orientation 157.

In one embodiment, there is a pair of opposed MMS sensors. One sensor,the PLUS sensor or first sensor 30 is aligned in the direction ofinterest. The other sensor, the MINUS sensor or second sensor 30′, isaligned opposite the direction of interest. The PLUS and MINUS sensorsare the same type of hardware component, just oriented in oppositedirections.

For each opposing pair, the output from the two (PLUS and MINUS) sensorsare averaged, using equation:COMBINED_RESULT=(PLUS−MINUS)/2

The errors from MMS sensors from both bias and hysteresis typedistortion are negated because the same deformation happens to both MMSsensors of the pair in opposite directions. The deformation error can beat least partially canceled out by the average of the combined result.Thus, an adjusted plastic bias value removes additional error of theplastic bias values, so that the position value of the processor module50 is a more accurate determination of actual X of the device.

The method may further include corrections based on the additionalcomponents, such as a magnetometer 80, as in FIGS. 1-2. The field datasignals can determine magnetic field strength, which may also affect theoscillation elements of the position sensors 30, 30′.

The present invention provides a method for determining position withimproved calibration. Under extreme conditions, such as hightemperatures, sensors can be calibrated to provide more accuratelocation information. The method allows for a terminal device toinitiate activity at the properly determined location. For example, amore accurate path of the drill bit on a bottom hole assembly can bemapped for a drill bit. Also, the sensitive movement of a handheldcontroller can be capture for more accurate movement simulated in avideo game. The position value based on orientation and location data ismore accurate with the calibration of the present invention. The presentinvention can account for high temperature conditions of a wellbore orheat sinks from a computer system.

The method and system of the present invention calibrate a sensor,particularly an MMS sensor. Although relatively simple and inexpensive,the durability and reliability of MMS sensors has prevented the adoptionof this micro-machine technology in many technical fields. Bias errorsand hysteresis errors could not be addressed with current systems. Theparticularities of such small and sensitive parts required extraaccommodations to insure reliability of the components. Certainconditions, such as temperature, had to be avoided in order to rely onthe data from these MMS sensors. With the present invention, an MMSsensor can now be calibrated to accurately determine position. Activitycan be initiated at a particular location determined by a calibrated MMSsensor.

The present invention provides a method for generating a plastic biasvalue for calibrating an MMS sensor. Beyond the prior art factorcalibration based on the effects of temperature, the present inventiongathers additional data and generates a different value to refine thereadings from the sensor. The plastic bias value accounts fortemperatures experienced by the sensor, time duration at eachtemperature, and the orientation or gravity value being detected duringthe exposure to those temperatures. The history of sensor can beconsidered so that bias and hysteresis errors no longer reduce thereliability of the sensor. For an MMS sensor, the plastic bias valuescan be used to form a plastic bias model, which can be used for a batchof MMS sensors assembled under the same conditions. Although the singlehistory of all plastic bias values of one MMS sensor will provide themost accurate data for that one MMS sensor, there is still utility forcreating a plastic bias model for all MMS sensors in the batch fromwhich the one MMS sensor was taken.

The present invention provides a method for generating an adjustedplastic bias value further correcting position values based on positiondata signals of two MMS sensors in opposite orientations. In addition tocorrecting for bias and hysterersis errors, the adjusted plastic biasvalue accounts for errors due to different gravity on the pair ofsensors. With opposing orientations, the effect of gravity on theposition sensors can be at least partially canceled out. Thetemperatures, time duration at each temperature for each sensor, andposition of each MMS sensor can be used to further cancel out errors dueto gravity on the MMS sensors. The opposing orientations allow thesubtraction of errors due to the different effect of gravity, when thesensors are in opposite orientations.

Prior art factory calibrations based on temperature remain compatiblewith the present invention. When the plastic bias value is determined tocalibrate the MMS sensor after a factory calibration, the sensorreadings still correct the sensor for bias and hysteresis andtemperature. When the plastic bias value is determined concurrent withthe factory calibration, the heating and cooling of the factorycalibration are incorporated into the plastic bias values of the sensor.When the plastic bias value continues to be used to calibrate the MMSsensor, the sensor readings still correct the sensor for bias andhysteresis.

In an embodiment of the present invention, the sensor is continuouslycalibrated with a plastic bias value. The real time history of theexposure of the sensor is used to calibrate so that the sensor readingsare the most accurate to exactly what conditions were experienced by thesensor. For an MMS sensor, the reliability problems due to hightemperature exposure, bias and hysteresis are now addressed so that MMSsensors can be used in more diverse applications. The activitiesinitiated at the determined position have increased accuracy, specificto the conditions exposed to the sensor. The prior art models andextrapolations are no longer the sole basis for error correction andcalibration. Furthermore, sustained activities, such as drilling, can betracked with the increased accuracy, such that the wellbore formed canbe mapped with better reliability. Real time navigation through theformation is guided by accurate position information, instead of beingguided by projections and theoretical models. The continuouslycalibrated MMS sensor actively adjusts sensor readings for advantagesand benefits beyond the prior art factory calibrations and prior artmultiple sensor arrangements.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof. Various changes in the details ofthe illustrated structures, construction and method can be made withoutdeparting from the true spirit of the invention.

We claim:
 1. A system for determining position, said system comprising: a first position sensor being comprised of a first oscillation element having a first range of displacement in a first set direction according to gravity in a first orientation, said first position sensor generating a first position data signal; a second position sensor being comprised of a second oscillation element having a second range of displacement in a second set direction according to gravity in a second orientation, said second position sensor generating a second position data signal, said second orientation being opposite said first orientation; a temperature sensor detecting a temperature data signal and being in proximity to said first position sensor and said second position sensor; a processor module being in communication with said first position sensor, said second position sensor, and said temperature sensor, said processor module receiving said first position data signal, said second position data signal, and said temperature data signal, said processor module generating a position value based on said first position data signal, said second position data signal, and said temperature data signal; a memory module being in communication with said processor module, said memory module storing said first position data signal, second position data signal, said temperature data signal, and said position value; a terminal device being in communication with said processor module and receiving said position value, said terminal device being comprised of a control means for activity corresponding to said position value; and another pair of position sensors, each position sensor of said another pair being comprised of another oscillation element having another range of displacement in another set direction according to gravity in opposing orientations, said another pair of position sensors generating a respective pair of position data signals, said another pair of position sensors being in proximity to said temperature sensor and being in communication with said processor module, said processor module receiving the respective pair of position data signals, said processor module generating said position value based on said first position data signal, said second position data signal, the respective pair of positional data signals, and said temperature data signal.
 2. The system for determining position, according to claim 1, wherein said processor module generates an adjusted plastic bias value based on said temperature data signal, time duration of said temperature data signal, said first position data signal, and said second position data signal, said position value being determined by said adjusted plastic bias value comprised of error correction based on said first position data signal and said second position data signal.
 3. The system for determining position, according to claim 1, wherein said terminal device is comprised of a downhole tool with a drilling assembly for oil and gas, said activity being drilling, said position value setting a location for drilling in a wellbore.
 4. The system for determining position, according to claim 1, wherein the opposing orientations of said another pair of position sensors are identical to opposing orientations of said first position sensor and said second position sensor.
 5. The system for determining position, according to claim 1, wherein the opposing orientations of said another pair of position sensors are different from opposing orientations of said first position sensor and said second position sensor.
 6. The system for determining position, according to claim 1, further comprising: a magnetometer being in proximity to said temperature sensor, being in communication with said processor module, and generating a field data signal, said processor module receiving said field data signal, said processor module generating an additional position value based on said field data signal, said position data signal, and said temperature data signal.
 7. A system for determining position, said system comprising: a first position sensor being comprised of a first oscillation element having a first range of displacement in a first set direction according to gravity in a first orientation, said first position sensor generating a first position data signal; a second position sensor being comprised of a second oscillation element having a second range of displacement in a second set direction according to gravity in a second orientation, said second position sensor generating a second position data signal, said second orientation being opposite said first orientation; a temperature sensor detecting a temperature data signal and being in proximity to said first position sensor and said second position sensor; a processor module being in communication with said first position sensor, said second position sensor, and said temperature sensor, said processor module receiving said first position data signal, said second position data signal, and said temperature data signal, said processor module generating a position value based on said first position data signal, said second position data signal, and said temperature data signal; a memory module being in communication with said processor module, said memory module storing said first position data signal, second position data signal, said temperature data signal, and said position value; a magnetometer being in proximity to said temperature sensor, being in communication with said processor module, and generating a field data signal, said processor module receiving said field data signal, said processor module generating an additional position value based on said field data signal, said position data signal, and said temperature data signal; and another magnetometer being in proximity to said temperature sensor, being in communication with said processor module, and generating another field data signal, said processor module receiving said another field data signal, said processor module generating said additional position value based on said field data signal, said another field data signal, said position data signal, and said temperature data signal.
 8. A method for determining position, the method comprising the steps of: assembling a first position sensor being comprised of a first oscillation element having a first range of displacement in a first set direction according to gravity in a first orientation; generating a first position data signal with said first position sensor; assembling a second position sensor being comprised of a second oscillation element having a second range of displacement in a second set direction according to gravity in a second orientation, said second orientation being opposite said first orientation; generating a second position data signal with said second position sensor; detecting a temperature data signal with a temperature sensor in proximity to said first position sensor and said second position sensor; communicating said first position data signal, said second position data signal, and said temperature data signal to a processor module being in communication with said first position sensor, said second position sensor, and said temperature sensor; generating a position value based on said first position data signal, said second position data signal, said temperature data signal and duration of temperature corresponding to said temperature data signal with said processor module; storing said first position data signal, said second position data signal, said temperature data signal, said duration of temperature, and said position value in a memory module in communication with said processor module; communicating said position value to a terminal device in communication with said processor module; and controlling activity of said terminal device corresponding to said position value, wherein, before the step of generating said position data signal, the method further comprises the steps of: raising said first position sensor at a null position of said oscillation element to an initial temperature for an initial amount of time; detecting an initial position data signal corresponding to an initial amount of displacement of said oscillation element at the initial temperature for the initial amount of time; returning said first position sensor to the null position according to data collected for the initial temperature and the initial amount of time; raising said first position sensor to said initial temperature for said initial amount of time; detecting another position data signal corresponding to another amount of displacement of said oscillation element at the initial temperature for the initial amount of time; and setting said position value based on said initial position data signal and said another position data signal.
 9. The method for determining position, according to claim 8, further comprising the steps of: generating an adjusted plastic bias value with said processor module based on based on said temperature data signal, said duration of said temperature, said first position data signal, and said second position data signal; and setting said position value according to said adjusted plastic bias value, wherein said first position data signal and said second position data signal are adjusted by said adjusted plastic bias value position value so as to determine said position value, said adjusted plastic bias value being comprised of error correction based on gravitational differences between said first position data signal and said second position data signal.
 10. The method for determining position, according to claim 8, wherein each position data signal corresponds to a measurement of a gravitational field on each oscillation element.
 11. The method for determining position, according to claim 9, wherein said first position data signal and said second position data signal are continually adjusted so as to continuously set said position value.
 12. The method for determining position, according to claim 8, further comprising the steps of: assembling another pair of position sensors, each position sensor of said another pair being comprised of another oscillation element having another range of displacement in another set direction according to gravity in opposing orientations; generating a respective pair of position data signals by said another pair of position sensors in proximity to said temperature sensor and in communication with said processor module; communicating the respective pair of position data signals to said processor module; and generating said position value with said processor module based on said first position data signal, said second position data signal, the respective pair of positional data signals, and said temperature data signal.
 13. The method for determining position, according to claim 12, further comprising the steps of: generating an adjusted plastic bias value with said processor module based on based on said temperature data signal, said duration of said temperature, said first position data signal, and second position data signal; and setting said position value according to said adjusted plastic bias value, wherein said position value is determined by said adjusted plastic bias value comprised of error correction based on said first position data signal and said second position data signal and respective position data signals of said another pair of position sensors.
 14. The method for determining position, according to claim 9, wherein each position data signal corresponds to a measurement of a gravitational field on each oscillation element.
 15. The method for determining position, according to claim 9, wherein said position value is continually set according to continuously corrections by said adjusted plastic bias value.
 16. The method for determining position, further comprising the step of: repeating the steps of claim 1 with different initial temperatures and different initial amounts of time.
 17. The method for determining position, according to claim 1, wherein the step of generating said position data signal comprises the steps of: raising said position sensor to a plurality of temperatures for a respective plurality of amounts of time; and generating a plurality of position data signals at each temperature for the respective amount of time, and wherein the step of generating said position value comprises the step of: setting each position value based on each position data signal, respective temperature, respective amount of time, any previous position data signal, any respective previous temperature, and any respective previous amount of time.
 18. The method for determining position, according to claim 17, wherein said position value is continually set according to respective continuous corrections by a previous position data signal, a corresponding previous temperature, and a corresponding previous amount of time. 